Study of the effects of intra-aortic balloon pumping in small animals. Our purpose is to define the applicability of a miniature intra-aortic balloon pump in puppies and lambs, for eventual use in infants and children. The development of an intra-aortic balloon pump has revolutionized the care of adult patients in post-cardiac surgical shock. Indications for balloon pumping include stabilizing cardiac patients prior to further diagnostic studies, relieving cardiac failure prior to further diagnostic studies, relieving cardiac failure prior to possible surgery as well as helping to wean them off the cardiopulmonary bypass and function as cardiac support in the postoperative period. Limitations of present hardware will be defined and the device modified to accomodate 3 to 5 Kg size animals. Methods of study will include closed and open chest techniques for insertion of the balloon in small animals. Ischemic heart failure, mitral insufficiency and a ventricular septal defect will be the pathological lesions produced for investigating the effects of the IAB. Methods for insertion and degrees of unloading in various pathologic states and the effects that intra-aortic pumping will have on the peripheral organs will be evaluated and defined. The significance of this study is that it will begin to identify 3 to 5 Kg candidates for the intra-aortic balloon pumping.